U.S. patent application number 13/718705 was filed with the patent office on 2014-10-09 for input common mode control using a dedicated comparator for sensor interfaces.
This patent application is currently assigned to MAXIM INTEGRATED PRODUCTS, INC.. The applicant listed for this patent is Maxim Integrated Products, Inc.. Invention is credited to Carlo Caminada, Roberto Casiraghi, Giorgio Massimiliano Membretti.
Application Number | 20140300415 13/718705 |
Document ID | / |
Family ID | 50911185 |
Filed Date | 2014-10-09 |
United States Patent
Application |
20140300415 |
Kind Code |
A1 |
Casiraghi; Roberto ; et
al. |
October 9, 2014 |
INPUT COMMON MODE CONTROL USING A DEDICATED COMPARATOR FOR SENSOR
INTERFACES
Abstract
Various embodiments of the invention allow for low-noise, high
performance input common mode voltage control in capacitive sensor
front end amplifiers. In certain embodiments overcome the
shortcomings of the prior art by implementing a full voltage swing
common mode voltage comparator in a parallel feed-forward path to
compensate large common mode input signal variations.
Inventors: |
Casiraghi; Roberto; (Milano,
IT) ; Caminada; Carlo; (Pregnana Milanese, IT)
; Membretti; Giorgio Massimiliano; (Milano, IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Maxim Integrated Products, Inc.; |
San Jose |
CA |
US |
|
|
Assignee: |
MAXIM INTEGRATED PRODUCTS,
INC.
San Jose
CA
|
Family ID: |
50911185 |
Appl. No.: |
13/718705 |
Filed: |
December 18, 2012 |
Current U.S.
Class: |
330/260 |
Current CPC
Class: |
H03F 3/45928 20130101;
G01P 15/0802 20130101; H03F 2203/45512 20130101; H03F 2200/261
20130101; H03F 3/45475 20130101; H03F 2203/45544 20130101; G01P
15/125 20130101 |
Class at
Publication: |
330/260 |
International
Class: |
H03F 3/45 20060101
H03F003/45 |
Claims
1. A comparator-based common mode voltage control circuit
comprising: a differential amplifier comprising a differential
amplifier input to receive a differential input signal that carries
an input common mode voltage; and an input common mode feedback
comparator comprising a first reference signal input to receive a
first reference signal, the feedback comparator compares the
differential input signal to the first reference signal to generate
a comparison result that indicates when the input common mode
voltage exceeds a predetermined threshold value with respect to the
first reference signal; and a correction signal that is applied to
the differential amplifier input to control the input common mode
voltage based on the comparison result.
2. The control circuit according to claim 1, wherein the comparator
is a dedicated rail-to-rail comparator capable of utilizing
substantially an entire output range of a power supply.
3. The control circuit according to claim 1, wherein the feedback
comparator applies the correction signal to the input of the
differential amplifier when the input common mode voltage exceeds a
predetermined threshold voltage.
4. The control circuit according to claim 1, further comprising a
first set of feedback capacitors coupled between an output of the
feedback comparator and the differential amplifier input.
5. The control circuit according to claim 4, wherein the first set
of feedback capacitors share a common terminal, the common terminal
being coupled to the output of the feedback comparator.
6. The control circuit according to claim 4, wherein the feedback
comparator delivers the correction signal via the first set of
feedback capacitors to the input of the differential amplifier to
compensate for an input common mode voltage variation.
7. The control circuit according to claim 6, wherein the correction
signal comprises a feed forward charge to adjust the input common
mode voltage.
8. The control circuit according to claim 1, further comprising a
feedback amplifier coupled to the differential amplifier input to
sense the input common mode voltage, the feedback amplifier
comprises a second reference voltage input to receive a second
reference voltage to determine a difference value between the
second reference voltage and the input common mode voltage and,
based on the difference value, the feedback amplifier generates a
common mode feedback signal that is applied to the differential
amplifier input to force the input common mode voltage to approach
the second reference voltage.
9. The control circuit according to claim 8, further comprising a
second set of feedback capacitors coupled between an output of the
feedback amplifier and the differential amplifier input.
10. The control circuit according to claim 9, wherein the second
set of feedback capacitors share a common terminal, the common
terminal being coupled to the output of the feedback amplifier.
11. The control circuit according to claim 10, wherein the feedback
comparator is a full swing comparator that serves as a feed-forward
current path for the feedback amplifier.
12. A differential detection circuit comprising: a sensor to
generate a differential sensor output signal, the differential
sensor output signal comprises an input common mode voltage; a
differential amplifier comprising first and second amplifier inputs
coupled to receive the differential sensor output signal, the
differential amplifier generates an output voltage representative
of the differential sensor output signal; and a feedback comparator
coupled in a loop configuration, the feedback comparator receives
the input common mode voltage, compares the differential input
signal to determine when the input common mode voltage exceeds a
predetermined threshold value with respect to a reference signal,
and generates a correction signal comparison result that is used as
a correction signal, the correction signal is applied to first and
second amplifier inputs to control the input common mode
voltage.
13. The differential detection circuit according to claim 12,
further comprising a feedback amplifier coupled in a first loop
between the sensor and the differential amplifier, the feedback
amplifier generates a common mode feedback signal that is applied
to the first and second amplifier inputs to dynamically control the
input common mode voltage.
14. The differential detection circuit according to claim 12,
wherein the sensor is a differential capacitive sensor, the
differential capacitive sensor comprises an input coupled to first
and second sensing capacitors, the first and second sensing
capacitors generate the differential sensor output signal.
15. The differential detection circuit according to claim 12,
wherein the feedback comparator delivers the correction signal via
a set of feedback capacitors to the input of the differential
amplifier to compensate for an input common mode voltage
variation.
16. The differential detection circuit according to claim 12,
wherein the correction signal comprises a feed forward charge.
17. A method to control an input common mode signal, the method
comprising: receiving an input common mode signal at an amplifier
input; sensing an input common mode voltage at the amplifier input
with a feedback comparator; comparing the input common mode voltage
to a first reference signal to determine whether the difference
exceeds a predetermined threshold value; generating a correction
signal to adjust the input common mode voltage; sensing the input
common mode signal at the input of the amplifier with a feedback
amplifier; comparing the input common mode voltage to a second
reference signal to determine a residual difference value; and
generating via a feedback capacitor a common mode feedback signal
that adjusts the input common mode voltage by forcing the input
common mode voltage to approach the second common mode reference
signal.
18. The method according to claim 17, wherein the generating the
correction signal comprises injecting a feed-forward current into a
differential feed-forward current path to adjust the input common
mode voltage.
19. The method according to claim 17, wherein the receiving the
input common mode signal occurs at a differential input of a
differential amplifier.
20. The method according to claim 17, wherein the input common mode
voltage is associated with an output of a sensor circuit.
Description
BACKGROUND
[0001] A. Technical Field
[0002] The present invention relates to common mode controls and to
systems, devices, and methods of controlling common mode voltage in
capacitive inertial sensor circuits.
[0003] B. Background of the Invention
[0004] Capacitive sensing circuits are used in gyroscopes, pressure
sensors, accelerometers, etc. to sense a change in capacitance
value caused by a linear or rotational movement. A differential
change can be detected by a differential operational amplifier that
outputs a proportional voltage, which then can be converted into
the desired physical quantity to be detected, for example,
rotation, pressure, or acceleration.
[0005] A capacitive sensing circuit operates through a driving
signal, like a voltage step, provided to a capacitive sensor and
the front end amplifier that reads and amplifies the sensor signal.
Typically, a fully differential input charge amplifier is used
since fully differential amplifiers are more reliable, accurate,
and relatively immune to noise generated by the power supply.
However, fully differential charge amplifiers generally require
control of the input common mode voltage through a dedicated
circuit, which can have a significant negative impact on the
amplifier's performance. The fully differential front end charge
amplifier and its common mode voltage control for the capacitive
inertial sensor are often implemented using switch-capacitor
circuits.
[0006] Switch-capacitor input common mode voltage control circuits
require a relatively a large feedback capacitance that increases
the total input front end capacitance and thereby increases system
noise and decreases the amplifier's performance. In addition, the
inability of the common mode feedback amplifier to quickly and
precisely recover the desired common mode voltage reduces the
maximum available operation speed of the front end electronics.
What is needed are common mode voltage controls that overcome the
above-described limitations.
SUMMARY OF THE INVENTION
[0007] Various embodiments of the invention provide a low noise
approach for input common mode voltage control in capacitive sensor
front end electronics. In particular, certain embodiments of the
invention allow system integrators to minimize overall amplifier
input capacitance and thereby optimize amplifier noise
performance.
[0008] Certain embodiments of the invention take advantage of a
full voltage swing common mode voltage comparator circuit that is
configured in parallel to a common mode feedback control circuit to
correct for most of the input common mode voltage change caused by
the stimulus that drives the capacitive sensor. The comparator
circuit acts as a parallel feed-forward branch that helps to more
rapidly and efficiently compensate common mode input signal
variations to optimize overall system performance.
[0009] Certain features and advantages of the present invention
have been generally described here; however, additional features,
advantages, and embodiments are presented herein will be apparent
to one of ordinary skill in the art in view of the drawings,
specification, and claims hereof. Accordingly, it should be
understood that the scope of the invention is not limited by the
particular embodiments disclosed in this summary section.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Reference will be made to embodiments of the invention,
examples of which may be illustrated in the accompanying figures.
These figures are intended to be illustrative, not limiting.
Although the invention is generally described in the context of
these embodiments, it should be understood that it is not intended
to limit the scope of the invention to these particular
embodiments.
[0011] FIG. 1 illustrates a prior art charge amplifier front end
circuit for differential capacitive sensors.
[0012] FIG. 2 illustrates a prior art front end electronics
architecture of a common mode voltage control using a common mode
feedback amplifier.
[0013] FIG. 3 illustrates a prior art "Wheatstone bridge" input
common mode control circuit.
[0014] FIG. 4 is a general illustration of a typical "Wheatstone
bridge" circuit.
[0015] FIG. 5 illustrates a comparator-based common mode voltage
control circuit according to various embodiments of the
invention.
[0016] FIG. 6 is a flowchart of an illustrative process for noise
cancellation in accordance with various embodiments of the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] In the following description, for the purpose of
explanation, specific details are set forth in order to provide an
understanding of the invention. It will be apparent, however, to
one skilled in the art that the invention can be practiced without
these details. One skilled in the art will recognize that
embodiments of the present invention, described below, may be
performed in a variety of ways and using a variety of means. Those
skilled in the art will also recognize that additional
modifications, applications, and embodiments are within the scope
thereof, as are additional fields in which the invention may
provide utility. Accordingly, the embodiments described below are
illustrative of specific embodiments of the invention and are meant
to avoid obscuring the invention.
[0018] Reference in the specification to "one embodiment" or "an
embodiment" means that a particular feature, structure,
characteristic, or function described in connection with the
embodiment is included in at least one embodiment of the invention.
The appearance of the phrase "in one embodiment," "in an
embodiment," or the like in various places in the specification are
not necessarily referring to the same embodiment.
[0019] Furthermore, connections between components or between
method steps in the figures are not restricted to connections that
are affected directly. Instead, connections illustrated in the
figures between components or method steps may be modified or
otherwise changed through the addition thereto of intermediary
components or method steps, without departing from the teachings of
the present invention.
[0020] In this document the terms "sensor" and "sensing circuit"
are used interchangeably.
[0021] FIG. 1 illustrates a prior art charge amplifier front end
circuit for differential capacitive sensors. FIG. 1 exemplifies the
basic functionality of a fully differential front end charge
amplifier 100 commonly used in capacitive sensors applications.
[0022] A voltage stimulus, V.sub.D, is applied, typically in the
form of a pulse function, at terminal 102 of sensor 104. The
voltage stimulus generates, at the input of charge amplifier 108,
both a differential signal and a common mode signal. The generated
common mode signal does not contribute to the desired readout.
Variations in the common mode signal constitute undesirable
disturbances. In some instances, the common mode voltage may assume
such high values as to saturate the input common mode voltage range
of charge amplifier 108. Since amplifiers are generally designed to
work within their linear range, once charge amplifier 108 is
saturated, it can no longer properly function in amplifying the
differential signal. Typically, an input common mode feedback
control circuit 110 is employed to prevent the common mode voltage
level at the input of charge amplifier 108 from changing
excessively from the desired V.sub.CM.sub.--.sub.REF value 111.
[0023] In addition, parasitic capacitance C.sub.P 112, 113 exists
at input terminal 105, 106 of fully differential charge amplifier
108. Parasitic input capacitance 112, 113 includes both sensor and
front end amplifier parasitic capacitances. The effect of parasitic
capacitance 112, 113 is to increase the total input capacitance of
amplifier 108. Since noise performance of capacitive sensor front
end electronics is very sensitive to input capacitance, parasitic
capacitance 112 and 113 should be minimized in order to reduce the
degradation of noise performance.
[0024] The input noise of front end amplifier 108 is amplified at
the output 118 by a factor proportional to
(C.sub.P+C.sub.F+C.sub.0)/C.sub.F, wherein C.sub.F is the
capacitance value of feedback capacitor 115, 116. The signal gain,
which is defined as the ratio of the output voltage 118 of charge
amplifier 108 to the capacitance variation of capacitive sensor
104, is proportional to .delta.C/C.sub.F. One skilled in the art
will recognize that, at the one hand, small capacitance values
C.sub.F of feedback capacitor 115, 116 are desirable to achieve
increased signal gain but, on the other hand, a small C.sub.F value
leads to high parasitic input capacitance 112, 113 that severely
impacts noise gain. Therefore, minimizing the total input
capacitance of fully differential charge amplifier 108 is crucial
to minimizing system noise and increasing overall system
performance.
[0025] FIG. 2 illustrates a prior art front end electronics
architecture of a common mode voltage control using a common mode
feedback amplifier. The topology in front end circuit 200 depicted
in FIG. 2 is used in certain sensor applications that require
common mode voltage control, such as in a fully differential
switched-capacitor amplifier circuit. Differential capacitive
sensor 204 receives a driving signal V.sub.D at terminal 202. The
stimulus signal is a voltage step function that drives a charge
through sense capacitors 205 and 206 changing the common mode
voltage at front end amplifier inputs. The charge is equivalent to
the amplitude of the voltage of the stimulus signal multiplied by
the capacitance of sense capacitor 205, 206. Common mode feedback
amplifier 225 must inject charge to compensate for the common mode
voltage change at input terminal 217, 218. Ideally, the voltage at
input terminal 217, 218 remains constant at all times.
[0026] The charge that can be compensated for by common mode
feedback amplifier 225 is equal to the dynamic output range of
amplifier 225 multiplied by the capacitance value of feedback
capacitor 226, 227. The dynamic output range of amplifier 225 is
limited to a value less than the power supply voltage. The
limitation of the output range of amplifier 225 requires a large
capacitance value of feedback capacitor 226, 227 in order to
sufficiently compensate for the charge injected by the stimulus
signal V.sub.D. The minimum capacitance value of feedback capacitor
226, 227 depends on sense capacitor 205, 206 and the voltage
V.sub.D applied to terminal 202. Unfortunately, the capacitance of
feedback capacitor 226, 227 significantly increase the total input
capacitance, which increases the amplified noise and results in a
degradation of the noise performance of front end amplifier 208. In
contrast, some embodiments of the current invention use a low
capacitance input common mode voltage control approach employing a
rail-to-rail comparator circuit.
[0027] FIG. 3 illustrates another prior art input common mode
control circuit. The topology in FIG. 3 is a prior art capacitive
"Wheatstone bridge" common mode voltage control circuit having an
optional input common mode feedback amplifier. Driving step voltage
VD 328 of equal magnitude but opposite polarity with respect to
stimulus step voltage V.sub.D 302 that is applied to sensing
capacitor 305, 306 is applied to control capacitor C.sub.p0 326,
327. Control capacitor C.sub.p0a 326, 327 serves as a passive
common mode control circuit 332. This topology takes advantage of
the properties of the common Wheatstone bridge depicted in FIG. 4.
In capacitive Wheatstone bridge common mode voltage control circuit
300, all fixed resistors of the Wheatstone bridge are replaced with
fixed control capacitors C.sub.p0 326, 327, and all variable
resistors of the Wheatstone bridge are replaced with variable
capacitor 305, 306 of sensor 304.
[0028] FIG. 4 is a general illustration of a typical "Wheatstone
bridge" circuit. In a perfectly compensated configuration, the
value of fixed resistor 404 is adjusted to match the value of
typical variable resistor R.sub.0 402, such that the output voltage
V.sub.OUT is a differential output proportional to the amplitude of
voltage V.sub.D and the common mode voltage at terminals 405, 406
is set at the desired level.
[0029] Returning now to the capacitive Wheatstone bridge topology
shown in FIG. 3. This circuit comprises an open loop system that
does not sense the input of amplifier 308. Rather, it applies an
open loop correction to the differential signal without regard to
the voltage variations present at the input of amplifier 308. One
problem with this design is that sensing capacitance C.sub.0 of
sensing capacitor 305, 306 is generally unknown. The capacitance of
control capacitor C.sub.p0 326, 327 could be designed to match a
typical value of sensing capacitance C.sub.0.
[0030] A further drawback of the capacitive Wheatstone bridge
design is timing skew error that is caused when the two step
voltages V.sub.D and VD at 302 and 328, respectively, are applied
with a timing delay relative to each other. Unavoidable variations
in the manufacturing process may result in different delays for the
two step voltages. The resulting timing skew error, however short,
at the amplifier input must be accounted for and controlled to
avoid unwanted excessive input common mode voltage pulse
variations. Various embodiments of the present invention overcome
the limitation of timing skew control of the capacitive Wheatstone
bridge design and other prior art solutions.
[0031] FIG. 5 illustrates a comparator-based common mode voltage
control circuit according to various embodiments of the invention.
Fully differential detection circuit 500 is a comparator-based
common mode voltage control circuit comprising optional active
input common mode feedback (ICMFB) amplifier 514. Detection circuit
500 comprises sensor 502, front end amplifier 540 comprising
feedback capacitor 524, 526, input common mode feedback comparator
(ICMFBC) 518 comprising feedback capacitor 510, 511, and ICMFB
amplifier 514 comprising feedback capacitor 512, 513. The details
of ICMFBC 518 are omitted for clarity. Sensor 502 may be any sensor
capable of producing a differential output signal.
[0032] As shown in FIG. 5, differential capacitive sensor 502
receives driving signal V.sub.D 506. Signal V.sub.D 506 is, for
example, a voltage step that is applied to sensor 502 to drive a
charge through a pair of sense capacitors 503, 504. The charge is
proportional to driving signal V.sub.D 506 multiplied by the
variance in capacitance of sense capacitors 503, 504. Sense
capacitors 503, 504 measure a differential capacitance that results
from a linear or rotational movement of electrodes disposed within
sensor 502. The resulting capacitive imbalance of sense capacitors
503, 504 from a reference capacitance that sensor 502 would assume
at rest, causes both an increase in the value of capacitor 503 and
a decrease of the capacitance of capacitor 504 by an equal amount.
Sensor 502 detects the mismatch of sense capacitors 503, 504 as a
differential change and, in response thereto, generates a
differential output signal. The differential output signal of
sensor 502 is received at the input of differential front end
amplifier 540.
[0033] A first output terminal of sensor 502 couples sense
capacitor 503 to non-inverting input terminal 508 of front end
amplifier 540. A second output terminal of sensor 502 couples sense
capacitor 504 to inverting input terminal 509 of front end
amplifier 540. Amplifier 540 receives the differential output
signal, e.g., a voltage that is proportional to the capacitive
change in sensor 502, and generates output voltage signal 544 from
which the desired physical quantity to be detected can be derived.
The output of front end amplifier 540 is fed back to the respective
input 508, 509 via feedback capacitor 524, 526, which serves as
integration capacitor in generating output voltage signal 544.
Detection circuit 500 further comprises ICMFB amplifier 514 and
full swing ICMFBC 518.
[0034] ICMFBC 518 is coupled between sensor 502 and front end
amplifier 540 and comprises two differential inputs that are
coupled to respective non-inverting and inverting input terminals
508, 509 of amplifier 540. ICMFBC 518 further comprises a reference
input terminal coupled to receive reference voltage 522. Feedback
voltage 538 of ICMFBC 518 is coupled to input terminals 508, 509 of
front end amplifier 540 via feedback capacitors 510, 511. Feedback
capacitors 510, 511 share a common terminal that is coupled to
feedback voltage 538 at the output of ICMFBC 518.
[0035] The precise value of feedback capacitor 510, 511 of ICMFBC
518 may be difficult to determine due to variations of sensor 502,
for example, during the manufacturing process. In one embodiment,
optional ICMFB amplifier 514 is used to precisely control the input
common mode voltage. ICMFB amplifier 514 is an active circuit that
is coupled, in a first loop configuration, between sensor 502 and
front end amplifier 540. Amplifier 514 comprises two differential
inputs that are coupled to non-inverting and inverting input
terminals 508, 509 of amplifier 540, respectively, and a reference
input terminal coupled to reference potential 520. Feedback voltage
536 of amplifier 514 is coupled to the input terminals of front end
amplifier 540 via feedback capacitor 512, 513. Feedback capacitors
512, 513 share a common terminal with each other, the common
terminal being coupled to feedback voltage 536 at the output of
ICMFB amplifier 514. Amplifier 514 detects a voltage difference
between non-inverting and inverting input terminals 508, 509 of
front end amplifier 540 and outputs feedback voltage 536 to
compensate the common mode voltage variation not perfectly
recovered by ICMFBC 518.
[0036] In one embodiment, comparator 518 is a full swing comparator
that serves as a feed-forward branch for ICMFB amplifier 514.
ICMFBC 518 may be implemented as a dedicated rail-to-rail
comparator that utilizes the entire power supply range to
compensate for the input common mode change thereby providing for a
fast recovery. Comparator 518 compares the common mode voltage of
non-inverting and inverting input terminals 508, 509 of amplifier
540 with reference voltage 522. Once the input common mode voltage
difference from the desired level exceeds a predetermined threshold
value, ICMFBC 518 quickly reacts by delivering a charge that is fed
back to the input of amplifier 540 to compensate for the common
mode input variation. For example, ICMFBC 518 may be designed to
apply a correction signal to the common mode signal when the input
common mode voltage variation threshold exceeds 10 mV to bring the
variation below the threshold of the comparator. ICMFBC 518 is
relatively faster than ICMFB amplifier 514. Additionally, since
ICMFBC 518 utilizes the rail-to-rail output dynamic range, it can
recover the common mode voltage signal that it detects at the
inputs of front end amplifier 540 relatively faster due to the
lower input capacitance when compared to prior art designs.
[0037] Further, when ICMFB amplifier 514 is used to precisely
control the input common mode level variations, it needs to
generate a reduced amount of charge to overcome the common mode
voltage variations than without comparator 518. This allows for a
reduction in common mode feedback capacitors 512, 513 when compared
with prior art designs.
[0038] Another benefit is that the addition of ICMFBC 518 allows
amplifier 514 to have a lower bandwidth than prior art designs. Yet
another benefit of adding ICMFBC 518 is that, unlike in the
Wheatstone bridge topology of FIG. 3 discussed above, no accurate
of control the timing skew between the signal applied to the sensor
and the additional signal of opposite polarity applied to the
bridge capacitors is required. This significantly simplifies the
re-design and tuning of sensor 502 since timing skew errors do not
affect the threshold voltage and, therefore, do not have to be
taken into consideration.. Instead, detection circuit 500 can be
designed to react to a predetermined voltage threshold to control
the input common mode variation. One skilled in the art will
appreciate that different implementations of ICMFBC 518 are
possible. Comparator 518 may, for example, be implemented as a
clock comparator.
[0039] FIG. 6 is a flowchart of an illustrative process to control
an input common mode voltage in accordance with various embodiments
of the invention. The process for controlling an input common mode
signal starts at step 602 when a differential amplifier receives an
input common mode signal at a differential input, for example, from
the output of a sensor circuit. In one embodiment, the differential
amplifier is a fully differential amplifier.
[0040] At step 604, an input common mode comparator senses the
input common mode voltage at the differential input of the
differential amplifier.
[0041] At step 606, the input common mode comparator compares the
input common mode voltage to a first common mode reference voltage
to determine whether the difference exceeds a predetermined
threshold value.
[0042] At step 608, the input common mode comparator generates a
correction signal by injecting a feed-forward current into a
differential feed-forward current path to adjust the input common
mode voltage.
[0043] At step 610, an input common mode amplifier senses the input
common mode signal at the input of the differential amplifier.
[0044] At step 612, the input common mode amplifier compares the
input common mode voltage to a second common mode reference voltage
to determine a residual difference value.
[0045] Finally, at step 614, input common mode amplifier generates
a common mode feedback signal to adjust the input common mode
voltage via a feedback capacitor coupled in a feedback loop to
force the input common mode voltage to approach the second common
mode reference voltage.
[0046] It will be appreciated by those skilled in the art that
fewer or additional steps may be incorporated with the steps
illustrated herein without departing from the scope of the
invention. No particular order is implied by the arrangement of
blocks within the flowchart or the description herein.
[0047] It will be appreciated that the preceding examples and
embodiments are exemplary and are for the purposes of clarity and
understanding and not limiting to the scope of the present
invention. It is intended that all permutations, enhancements,
equivalents, combinations, and improvements thereto that are
apparent to those skilled in the art, upon a reading of the
specification and a study of the drawings, are included within the
scope of the present invention. It is therefore intended that the
claims include all such modifications, permutations, and
equivalents as fall within the true spirit and scope of the present
invention.
* * * * *